It is well documented that atrial fibrillation (AF), either alone or as a consequence of other cardiac disease, continues to persist as the most common type of cardiac arrhythmia. In the United States, AF currently affects an estimated two million people, with approximately 160,000 new cases being diagnosed each year. The cost of treatment for AF alone is estimated to be in excess of $400 million worldwide each year.
AF may be treated using several approaches. Pharmacological treatment is initially the preferred approach, first to maintain normal sinus rhythm. Certain antiarrhythmic drugs, like quinidine and procainamide, can reduce both the incidence and the duration of AF episodes but typically fail to maintain sinus rhythm in the patient. Cardioactive drugs, like digitalis, Beta blockers, and calcium channel blockers, are used to control AF by restoring the heart's natural rhythm and limiting the natural clotting mechanism of the blood. However, antiarrhythmic drug therapy often becomes less effective over time. In addition, antiarrhythmic drugs can have severe side effects, including pulmonary fibrosis and impaired liver function.
A surgical approach known as the “MAZE” procedure was developed, which effectively creates an electrical maze in the atrium and precludes the ability of the atria to fibrillate. Utilizing the MAZE procedure, a surgeon makes strategically placed incisions through the wall of the atrium with a scalpel and then sews the cuts back together, creating a scar pattern. The scars interrupt the conduction routes of the most common reentrant circuits and direct the sinus impulses from the sinoatrial node to the atrioventricular node along a specified route. However, while effective to ablate medically refractory atrial fibrillation, the MAZE procedure is expensive and complicated to perform. Moreover, because the MAZE procedure must be performed as an open-chest procedure, it significantly increases the risk of complication and trauma to the patient.
Minimally invasive techniques were next developed to minimize the long hospital stays associated with open-chest procedures. Typically, these devices have an elongate, highly-flexible shaft with a steerable distal end for negotiating a path through the body of a patient. Rigid shaft devices are used in more invasive procedures where a more local opening or direct access to a treatment site is available or created.
The foregoing devices are intended to ablate through the full thickness of the cardiac wall, and thus create a risk associated with damaging structures within or on the outer surface of the cardiac wall. To address these problems ablation devices were developed which include opposing blade members that ablate tissue from both sides of the cardiac wall. For example, U.S. Pat. No. 5,443,463 to Stern et al., U.S. Pat. No. 5,733,280 to Avitall; U.S. Pat. No. 6,161,543 to Cox et al.; and U.S. Pat. No. 6,517,536 to Hooven et al. all describe techniques for ablating tissue of organs or vessels having opposing walls and also disclose ablation devices having clamping members with opposing jaws that clamp a treatment site therebetween.
Particularly, Stern et al. disclose a method and apparatus for selectively coagulating blood vessels or tissue containing blood vessels that involves the placement of the blood vessels or tissue between the prongs of a forceps with the jaws of the forceps containing a plurality of electrodes which are energized by radio-frequency power. A plurality of sensors are associated with the electrodes and are in contact with the vessels or tissue in order to measure the temperature rise of the tissue or blood vessels and to provide feedback to the radio-frequency power in order to control the heating and perform coagulation of the vessels or tissue.
Avitall discloses probe devices suitable for epicardial mapping and ablation. In one embodiment, the probes are designed to be used directly in an open chest mode during cardiac surgery for the rapid creation of linear lesions on an exposed heart. In another embodiment, the probes are designed to capture myocardial tissue between parallel probe members to create lesions through the tissue thickness. A first probe member may be used to penetrate the myocardial tissue to the inside of an atrial chamber. The first probe member may cooperate with a second probe member disposed on the outer surface.
Cox et el. disclose a system for transmurally ablating heart tissue that includes an ablating probe having an elongated shaft positionable through the chest wall and into a transmural penetration extending through a muscular wall of the heart and into a chamber thereof. The shaft includes an elongated ablating surface for ablating heart tissue. Furthermore, the system includes a sealing device fixable to the heart tissue around the transmural penetration for forming a hemostatic seal around the probe to inhibit blood loss therethrough.
Finally, Hooven et al. disclose a method and apparatus for transmural ablation using an instrument containing two electrodes or cryogenic probes. A clamping force is exerted on the two electrodes or probes such that tissue is clamped therebetween. Bipolar RF energy is then applied between the two electrodes, or the probes are cryogenically cooled, thus ablating the tissue therebetween. As illustrated in FIG. 9 of Hooven et al., the electrodes or cryogenic probes are provided on the center portion of solid jaw members. Consequently, the surgeon cannot visualize the tissue that is clamped between these jaw members during treatment. Therefore, a monitoring device is provided that measures a suitable parameter, such as impedance or temperature, and indicates when the tissue between the electrodes has been fully ablated.
Based on the foregoing, it is apparent that the systems disclosed in Stern et al., Avitall, Cox et al., and Hooven et al. do not allow the surgeon to assess transmurality of a lesion without relying on, for example, temperature or impedance, or without having to first remove the device from the tissue site.
One common element of the devices disclosed in Stern et al., Avitall, Cox et al., and Hooven et al. is that they include rigid members/shafts to facilitate reaching the tissue treatment site. Although a rigid shaft can be provided with a predetermined shape, one must select a device with a rigid shaft that has the most appropriate shape for positioning the working portion of the device in contact with the treatment site in view of the particular anatomical pathway to be followed in the patient. It will be appreciated that a large inventory of devices having rigid shafts may be required to accommodate the various treatment sites and patient anatomies. For example, Cox el al. describe a variety of rigid probe shapes. Further, for a patient having a relatively uncommon anatomic configuration and/or a difficult to reach treatment site, all rigid devices of an existing set may have less than optimal shapes for positioning. This may impair the prospects of successfully carrying out the treatment procedure. For an ablation device which must bear against tissue at the remote region to create lesions, the contour followed by the device in reaching the target site will in general further restrict the direction and magnitude of the movement and forces which may be applied or exerted on the working portion of the device to effect tissue contact and treatment.
U.S. Publication No. 2004/0254606 to Wittenberger et al. discloses a shaft assembly that has malleability such that the shaft assembly retains a first shape until manipulated to a second shape thus purportedly overcoming the problems associated with the foregoing inventions. When positioned, the Wittenberger et al. device includes sensor mechanisms that measure temperature and impedance that are designed to help the surgeon assess transmurality. The resulting temperature or impedance readings provide an indication to the surgeon of the transmurality of the lesion. However, these electrode systems may be prone to breaking down while in use and require an interpolation of transmurality. For example, Wittenberger et al. disclose that transmurality may be ascertained when the temperature sensor detects a temperature of −40 degrees Centigrade for two minutes but that time and temperature may be different for different types, conditions and thicknesses of tissue. Therefore, the surgeon has to remove the clamp from the tissue to visualize whether or not transmurality of the lesion has been achieved. If not the clamp must then be positioned on the tissue again which may result in improper placement with additional tissue being subjected to the procedure, which tissue might not be fully ablated.
Therefore, a need exists for a surgical ablation device that includes a mechanism on the jaws that allows the surgeon to assess transmurality of the lesion without relying on temperature or impedance and without having to remove the clamp from the tissue site.